SOIL AND PLANT ANALYSIS (1+1)

Oxidation-reduction potential or Redox potential

Redox potential (Eh) is otherwise called oxidation reduction reaction. Oxidation is the addition of oxygen or removal of hydrogen. Reduction is the addition of hydrogen or removal of oxygen.

In oxidation process, energy is released, electron is donated, or loss of electrons occurs. In reduction energy is accepted or acceptance of electrons or gain of electrons. This is also called as electron acceptance process. The compound, which donates electron or hydrogen, is called hydrogen donor or electron donor. The compound, which that accepts electron is called electron acceptor.

A substance is said to be oxidized when it looses it’s electron or when it act as a hydrogen donor and a substance is said to be reduced when it gains electron or when it act as hydrogen acceptor. In any chemical reaction every oxidation or loss of electron is accompanied by reduction or gain of electron. This system is called electron transfer system. The oxidation–reduction is also called coupled hydrogenation or hydrogenation process.

Redox potential is defined as “the capacity or potentiality of a compound either to oxidize or to reduce a substance or compound and this is expressed by electron unit called mV.

In soil system, soil organic matter provides the energy for release of electron.
Higher oxidation – positive (+) volt
Higher reduction – negative (-) volt
The redox potential is denoted by the symbol Eh
Where E denotes energy
h = Poise (stability of the system)
Eh is one of the physicochemical characters of soil used to determine whether the soil is submerged or aerated. When the soil is oxidized or aerated then the Eh is +ve. Soil is in reduced condition then Eh is –ve.
Materials required:
1.Redox electrode
2.100 ml beaker

Procedure:

• Calibration procedure for relative mV measurement:Relative mV measurement calibration is normally used in ISE measurement. Where it is common to use the lowest concentration mV value as the base value for measurements. All subsequent measurement will then the based on that reference value.
• Press the mode key to enter the relative mV. The primary display shows absolute
• mV reading and the secondary display shows the temperature.
• Press CAL key to activate calibration mode. The CAL indicator will display on the LCD
• Adjust the base value required (182 mV) by using up and down keys.
• Press CON key to confirm the calibration. The CON indicator will flash for one second
• and will disappear. On disappearing the LCD will display zero mV reading.
• Now the meter is calibrated for relative mV measurement.
• Now insert the electrode into a beaker containing soil
• Press the CAL MEAS key so that the meter will return to the measurement mode. In this
• primary mode displays mV reading.

The display value is calculated as follows

Displayed value = Absolute mV readings – Relative mV base value